This invention relates to techniques for restoring subterranean formations which have been subjected to in situ leaching of uranium values.
Recovery of uranium values from subterranean formations involves in the usual methods the oxidation of insoluble tetravalent uranium into soluble uranyl complexes that may be drawn from the formation by leaching. The overall reaction in oxidative in situ leaching may be described as follows: EQU UO.sub.2 (S)+[O]+3HCO.sub.3.sup.- .fwdarw.UO.sub.2 (CO.sub.3).sub.3.sup.-4 +H.sup.+
As the source of carbonate ion, ammonium carbonate or ammonium bicarbonate is often used in the leach solution. Unfortunately, this results in the formation being contaminated with ammonium ions, thereby producing the potential of water pollution through contamination of aquifers flowing in or near the formation, as follows: EQU (NH.sub.4).sub.2 CO.sub.3 +Ca-clay.fwdarw.NH.sub.4 -clay+CaCO.sub.3
Following uranium leaching with ammonium solutions, restoration of the formation therefore must be undertaken. The most economical method of restoration consists of flushing the formation with fresh water. While this process continually leaches ammonia from the clay surfaces, it generally involves a long and sometimes incomplete restoration.